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NETISR(9)	       FreeBSD Kernel Developer's Manual	     NETISR(9)

     netisr -- Kernel network dispatch service

     #include <net/netisr.h>

     netisr_register(const struct netisr_handler *nhp);

     netisr_unregister(const struct netisr_handler *nhp);

     netisr_dispatch(u_int proto, struct mbuf *m);

     netisr_dispatch_src(u_int proto, uintptr_t	source,	struct mbuf *m);

     netisr_queue(u_int	proto, struct mbuf *m);

     netisr_queue_src(u_int proto, uintptr_t source, struct mbuf *m);

     netisr_clearqdrops(const struct netisr_handler *nhp);

     netisr_getqdrops(const struct netisr_handler *nhp,	u_int64_t *qdropsp);

     netisr_getqlimit(const struct netisr_handler *nhp,	u_int *qlimitp);

     netisr_setqlimit(const struct netisr_handler *nhp,	u_int qlimit);

     netisr_default_flow2cpu(u_int flowid);


     netisr_get_cpuid(u_int cpunumber);

     The netisr	kernel interface suite allows device drivers (and other	packet
     sources) to direct	packets	to protocols for directly dispatched or
     deferred processing.  Protocol registration and work stream statistics
     may be monitored using netstat(1).

   Protocol registration
     Protocols register	and unregister handlers	using netisr_register()	and
     netisr_unregister(), and may also manage queue limits and statistics
     using the netisr_clearqdrops(), netisr_getqdrops(), netisr_getqlimit(),
     and netisr_setqlimit().

     netisr supports multi-processor execution of handlers, and	relies on a
     combination of source ordering and	protocol-specific ordering and work-
     placement policies	to decide how do distribute work across	one or more
     worker threads.  Registering protocols will declare one of	three poli-

     NETISR_POLICY_SOURCE  netisr should maintain source ordering without
			   advice from the protocol.  netisr will ignore any
			   flow	IDs present on mbuf headers for	the purposes
			   of work placement.

     NETISR_POLICY_FLOW	   netisr should maintain flow ordering	as defined by
			   the mbuf header flow	ID field.  If the protocol
			   implements nh_m2flow, then netisr will query	the
			   protocol in the event that the mbuf doesn't have a
			   flow	ID, falling back on source ordering.

     NETISR_POLICY_CPU	   netisr will entirely	delegate all work placement
			   decisions to	the protocol, querying nh_m2cpuid for
			   each	packet.

     Registration is declared using struct netisr_handler, whose fields	are
     defined as	follows:

     const char	* nh_name	  Unique character string name of the proto-
				  col, which may be included in	sysctl(2) MIB
				  names, so should not contain whitespace.

     netisr_handler_t nh_handler  Protocol handler function that will be
				  invoked on each packet received for the pro-

     netisr_m2flow_t nh_m2flow	  Optional protocol function to	generate a
				  flow ID and set M_FLOWID for packets that do
				  not enter netisr with	M_FLOWID defined.
				  Will be used only with NETISR_POLICY_FLOW.

     netisr_m2cpuid_t nh_m2cpuid  Protocol function to determine what CPU a
				  packet should	be processed on.  Will be used
				  only with NETISR_POLICY_CPU.

     netisr_drainedcpu_t nh_drainedcpu
				  Optional callback function that will be
				  invoked when a per-CPU queue was drained.
				  It will never	fire for directly dispatched
				  packets.  Unless fully understood, this spe-
				  cial-purpose function	should not be used.

     u_int nh_proto		  Protocol number used by both protocols to
				  identify themselves to netisr, and by	packet
				  sources to select what handler will be used
				  to process packets.  A table of supported
				  protocol numbers appears below.  For imple-
				  mentation reasons, protocol numbers great
				  than 15 are currently	unsupported.

     u_int nh_qlimit		  The maximum per-CPU queue depth for the pro-
				  tocol; due to	internal implementation
				  details, the effective queue depth may be as
				  much as twice	this number.

     u_int nh_policy		  The ordering and work	placement policy for
				  the protocol,	as described earlier.

   Packet source interface
     Packet sources, such as network interfaces, may request protocol process-
     ing using the netisr_dispatch() and netisr_queue()	interfaces.  Both
     accept a protocol number and mbuf argument, but while netisr_queue() will
     always execute the	protocol handler asynchronously	in a deferred context,
     netisr_dispatch() will optionally direct dispatch if permitted by global
     and per-protocol policy.

     In	order to provide additional load balancing and flow information,
     packet sources may	also specify an	opaque source identifier, which	in
     practice might be a network interface number or socket pointer, using the
     netisr_dispatch_src() and netisr_queue_src() variants.

   Protocol number constants
     The follow	protocol numbers are currently defined:

     NETISR_IP	    IPv4

     NETISR_IGMP    IGMPv3 loopback

     NETISR_ROUTE   Routing socket loopback

     NETISR_AARP    Appletalk AARP

     NETISR_ATALK1  Appletalk phase 1

     NETISR_ATALK2  Appletalk phase 2



     NETISR_IPV6    IPv6


     NETISR_EPAIR   netstat(1),	epair(4)

     This manual page and the netisr implementation were written by Robert N.
     M.	Watson.

FreeBSD	9.2		       February	22, 2010		   FreeBSD 9.2


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